Modified 555 Timer IC Using Only Two Comparators

This paper proposed a modified 555 timer IC with only two comparators by eliminating the discharge transistor and SR flip-flop. A periodic square waveform can be generated by utilizing the interconnection of two comparators to provide ‘Set’ and ‘Reset’ conditions to each other. The simulation and experimental results confirm that the clock frequency generated by the modified 555 timer circuit is significantly higher and duty cycle adjustment can be made more precise and flexible than the commercially available 555 timer circuit. A frequency in the band of 1MHz to 89MHz can be generated by replacing the resistors, capacitor, and comparator specification in all possible configurations. As a result, a lower cost and higher efficiency on-chip reference clock generator can be realized to fulfill versatile future application needs.